Laserdiodes (LDs) may be used for compacts discs (CDs), other types of optical discs, laser scanners, and other applications. Like a light-emitting diode (LED), a LD employs a forward-biased p-n junction to generate light through electron-hole recombination. However, in an LED, photons are emitted by a process called spontaneous emission.
In contrast, LDs are capable of generating laser beams because they are designed to amplify light through an emission process referred to as stimulated emission. Stimulated emission occurs in a LD because a LD includes a cavity in which some of the surfaces are mirrored. The cavity is referred to as an “optical cavity”. When photons are emitted from the LD, most of the photons are reflected by the optical cavity, causing the photon density in the optical cavity to increase. In stimulated emission, each electron-hole pair recombines in the presence of a photon of the correct wavelength. When the electron-hole pair recombines, a photon is emitted having the same phase as the photon causing the emission. Accordingly, the photon emission for photons of the selected wavelength increases, and the electron-hole pair recombination rate increases.
A LD driver (LDD) is typically used to drive a LD. The LDD provides an output current to drive the LD. In response to the output current, the LD provides a laser beam, which may be used for reading information from an optical disc, and/or writing optical information to an optical disc.